Microelectromechanical systems (MEMS) are widely used in a variety of sensing applications. For example, vehicle or automotive applications may use MEMS sensors, such as accelerometers or gyroscopes, to determine when to deploy the vehicle airbag or activate a stability and/or traction control system. In addition, consumer electronics devices, such as video game controllers, personal media players, cell phones, and digital cameras, also use MEMS sensors in various applications to detect the orientation and/or respond to rotational movement of the device.
MEMS gyroscopes often employ a small vibrating mass which is driven to resonate within a two-dimensional plane, i.e., the plane of oscillation. When the plane of oscillation is rotated, the Coriolis force causes the vibrating mass to be displaced from the plane of oscillation by an amount proportional to the rate of rotation. In order to determine the rate of rotation, this displacement is measured and converted into an electrical signal which oscillates with the same resonant frequency as the vibrating mass. An in-phase component of this electrical signal is proportional to the rate of rotation. Due to imperfections in manufacturing of the vibrating mass, often, a large unwanted error signal is present as the quadrature component (e.g., shifted 90° relative to the rate of rotation signal component) of the electrical signal. Therefore, in order to determine the rate of rotation, the electrical signal is often demodulated using a carrier signal at the resonant frequency into an in-phase component and a quadrature component. In many systems, a closed-loop control system is created by modulating (or remodulating) the demodulated components in a feedback path and applying the remodulated signals to the vibrating mass to counter the displacement caused by the rotation.
Often, multipliers or mixers are used to multiply the electrical signals by sine and cosine components of the carrier signal to accomplish the demodulation and/or modulation. However, the multiplication circuitry introduces a phase shift in the feedback path of the closed-loop system. This phase shift can cause an unwanted quadrature component to drift into the in-phase component of the remodulated signal, and vice versa, which limits the ability of the feedback signal (or force applied to the vibrating mass) to accurately track the measured signal. In practice, the unwanted quadrature component signal can be several times larger than the full-scale in-phase component signal that represents the rate of rotation. Therefore, even a very small phase shift by the multiplication circuitry can prevent accurate measurement of the rate of rotation and produce unacceptable distortion and offset drift in the output of the gyroscope.